This is an epidemiologic program whose functions are to detect, evaluate and quantify adverse effects of drug use in humans. We propose: l) To continue selective case-control surveillance of illnesses resulting in hospital admission. 2) To further refine the methods so that adequate numbers of cases with conditions of concern can be rapidly accrued, as the need arises. 3) To expand the concept of selective case-control surveillance to the monitoring of conditions which are known frequently to be drug-induced (e.g. agranulocytosis). 4) To continue the case-control surveillance of congenital malformations in relation to drug use in pregnancy. 5) To continue monitoring cohorts of pediatric in-patients to determine incidence rates of adverse drug effects. 6) To follow cohorts of users, both of newly marketed and of established drugs, when necessary, or to mount ad hoc case-control studies. 7) To generate hypotheses in the surveillance data, and to test them; in addition, to use the surveillance data to test hypotheses from other sources. 8) To explore the utility of HMO's with computer-retrievable prescription data with a view to conduction validation studies of drug histories obtained by interview. 9) To explore the utility of HMO's that have computer-retrievable information both on drug prescriptions and illnesses as potential sources for generating hypotheses.